By the way, the quote in the post title appeared in the amicus brief filed by 172 Members of the U.S. House of Representatives and 40 U.S. Senators. Here's the context, showing something of the case law that makes this a powerful argument (to anyone who accepts the precedents and is willing to consider the legislative history):
DOMA is... unlike most other Acts of Congress in another critical respect: A clearly stated purpose for its enactment was to express moral disapproval of a disfavored minority group. Many proponents repeatedly stated their intent to "honor a collective moral judgment" reflecting "moral disapproval of homosexuality" (House Report at 15-16). Chairman Hyde explained, for example, that "most people do not approve of homosexual conduct * * * and they express their disapprobation through the law." 142 Cong. Rec. H7501 (July 12, 1996). Lead Senate sponsor Don Nickles likewise stated that "we find ourselves at the point today that this legislation is needed" because of the "erosion of values." 142 Cong. Rec. S4870 (May 8, 1996).
Those views no doubt reflect "profound and deep convictions," reflecting the "ethical and moral principles" of those who hold them. [Citation to Lawrence v. Texas]. But this Court has made clear that such "considerations do not answer the question before us." Ibid. No matter how sincerely held, such beliefs are not a constitutionally valid basis for enacting "a classification of persons undertaken for its own sake" and "den[ying] them protection across the board." [Citation to Romer v. Evans].